1. Field of the Invention
This invention relates to ophthalmic lens surfacing tools with particular reference to means for adapting blocked lenses to lens surfacing machinery.
2. Description of the Prior Art
Blocked ophthalmic lenses having semifinished surfaces requiring final precision grinding and polishing are traditionally pressed against preformed tools (laps) and oscillated thereover with force applied to the block. The block being customarily aligned with the optical center of the lens and thereby geometrically decentered in cases of larger lens sizes results in forces applied to the block being unevenly distributed over the lens-tool surfacing interface. This in turn causes uneven grinding and polishing of the lens surface. Uneven pressure in grinding, tends to introduce prismatic error into the ophthalmic correction desired to be provided by the finished lens while uneven pressure during polishing produces areas of incomplete finishing where least pressure is applied and/or requires prolonged polishing cycles. Incomplete polishing produces what is often referred to as "gray" areas rendering the lenses consumer rejectable while lengthy polishing times uneconomically tie up both equipment and manpower.
The problem being identifiable as a need to apply pressure uniformly over a lens-tool surfacing interface has heretofore lacked a practical solution. For example, deblocking after lens surface milling or generating and reblocking on geometrical center for fine grinding (lapping) and polishing would be unduly time consuming and uneconomical.
Lens blocking methods and apparatuses such as are disclosed in U.S. Pat. Nos. 2,603,922 and 2,748,548 for example suggest that more than one recess may be provided in a lens block for reception of block holding means during lens grinding. These references, however, fail to offer or suggest the universality needed to accurately geometrically center applied grinding or polishing forces in decentered blocking situations.
Accordingly, it is a principle object of the present invention to accomplish universal geometrical centering and distribution of grinding and polishing forces uniformly over lens-tool surfacing interfaces in all situations of lens block decentering normally encountered in the art.
To this end, it is an object of the invention to provide universally adjustable lens block adaptor means designed to receive and direct lens surfacing pressure geometrically centrally and uniformly over a lens-tool surfacing interface.
Other objects and advantages of the invention will become apparent from the following description.